1. Field of the Invention
This invention relates to a torque distributing apparatus that controls the torque distributing ratio to first and second output shafts from a power source.
2. Discussion of the Background
Japanese patent No. 3247484, for example, discloses a torque distributing apparatus that has a differential gear unit, a planetary gear set and a motor. The differential gear unit transmits an input torque to first and second output shafts while allowing differential rotation between the output shafts. The planetary gear set is arranged between the first and second output shafts. The motor is connected with the planetary gear set. When the motor drives the planetary gear set, the torque distributing apparatus provides differential rotation between the first and second output shafts. The motor controls torque to the planetary gear set so as to control the torque distributing ratio to the first and second output shafts from a power source, e.g. an engine. In the torque distributing apparatus, the planetary gear set has planetary gears that are carried by a planetary carrier and engage with a sun gear and a ring gear, and one of the sun and ring gears is connected with the motor as an input element of the motor torque. A speed change gear set is arranged beside the planetary gear set in order to compensate its gear ratio. The speed change gear set has the same construction as the planetary gear set, wherein the both sun gears or ring gears are connected with no relative rotation and another gear of the speed change gear set is fixed on the nonrotatable portion. The prior art, however, has difficulty in gaining a large reduction gear ratio of the planetary gear set. Thus it is necessary, for sufficient torque for providing the differential rotation, to increase the motor output or add an additional reduction gear set. In addition, since the planetary gears, sun gear and ring gear are arranged on the same plane, it is complicated to support the planetary carrier, sun gear and ring gear. Therefore the prior art has a large size and complicated assembling operation.
Another prior art, Japanese patent application publication No. 2006-112474, discloses a torque distributing apparatus whose controlling motor is disposed outside of a housing of the planetary gear set. The motor is connected to the planetary gear set via a reduction gear set so as to gain the sufficient torque for providing the differential rotation. However the prior art becomes large because of the reduction gear set. If the reduction gear set is downsized then, as a trade-off, the motor must be large to provide sufficient driving torque. In addition, since the motor projects from the housing, the torque distributing apparatus has a weight imbalance and may interfere with other parts installed in the underbody of a vehicle. Further, if the reduction gear set is provided with large reduction gear ratio in order to downsize the motor, when one wheel slips during driving on μ-split road and there occurs a large differential rotation between the wheels, over-speed of the motor may happen.